Background. Comparison of Leaching of PAHs from two Contaminated Soils under Varying Hydraulic Retention Time

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1 Comparison of Leaching of PAHs from two Contaminated oils under Varying Hydraulic Retention Time Background Hydraulic retention time, HRT, is an important parameter when conducting leaching experiments Anja Enell, Therese Nilsson and Per Warfvinge Department of Chemical Engineering Lund University HRT = the contact time between the liquid and the solid phase Background Background

2 Background Objectives To investigate which processes control leaching of PAHs from aged contaminated soil To investigate if leached concentrations from field contaminated soil, obtained by dynamic column leaching, can reach equilibrium concentrations at very short contact times To demonstrate that leaching of PAHs from aged contaminated soils can show significant differences in leaching behaviour, leachable concentrations and available amounts oil samples 1. Husarviken, tockholm, weden former gasworks plant ( ) coal tar, heavy metals, cyanide Parameters oil data Coal tar cont. soil Creosote cont. soil TOC % 16 3 ph water (1:10) Density kg/l (d.w.) Composition of soil (%) Coarse sand (>0.2 mm) Holmsund, Umeå, weden former impregnation facility ( ) creosote, As, Cu, Cr Fine sand ( mm) ilt ( mm) Clay (<0.002 mm) 5 5

3 Initial amounts Design of the leaching experiment PAH Abbreviation Coal tar cont. soil (mg/kg soil) Creosote cont. soil Fluorene FLU 7 ± ± 12 Phenanthrene PHE 61 ± ± 43 Anthracene ANT 60 ± ± 101 Fluoranthene FLU 221 ± ± 36 Pyrene PYR 177 ± ± Glass column 2. edimentation chamber 3. Filter 4. PE cartridge 5. Drop counting detector 6. Reservoir 7. Peristaltic pump Experimental set up Experimental flow rates and HRTs Glassware and stainless steel terilization, HgCl µm filter Husarviken (coal tar contaminated soil) Elevation difference of 38 m! Large proportion of medium to coarse material 0.5 kg soil High groundwater velocities

4 Experimental flow rates and HRTs HRTs, Husarviken Flow rates chosen for the experiments: L h -1 (Darcy velocities: m year -1 ) Husarviken, coal tar mdw.. ε HRT = Q ρ dw.. Q m d.w. ε ρ d.w. = flow rate = amount of sample material = porosity = density HRT =0.3 h x h x h x 1 HRT: h Leached concentrations, Husarviken FLU Leached concentrations, Husarviken FLU Mean value

5 Leached concentrations, Husarviken Modelling the column leaching Q c out = c w c=c 1 +dc O I release rate, flux dv L At the soil surface, c = c eq r = k m (c eq -c) c=c 1 O I -km C = C (1 e w eq *HRT ) L Q c in = 0 Modelling results Interpretation of k m FLU k m = ANT k m = cm 3 mol -1 D A km δ V k m = mass transfer coefficient (h -1 ) D = the diffusivity of the solute (cm 2 s -1 ) A = the sorbent surface area (cm 2 ) V = the pore water volume (cm 3 ) PHE k m = 2.31 Le Bas molar volume O r = k m (c eq -c) δ = the distance of the mass transfer (cm) I FLA k m = 5.13 L δ PYR k m = cm 3 mol -1

6 Interpretation of k m Interpretation of k m k m = mass transfer coefficient (h -1 ) k m = mass transfer coefficient (h -1 ) D A km δ V D = the diffusivity of the solute (cm 2 s -1 ) A = the sorbent surface area (cm 2 ) D A km δ V D = the diffusivity of the solute (cm 2 s -1 ) A = the sorbent surface area (cm 2 ) V = the pore water volume (cm 3 ) V = the pore water volume (cm 3 ) O r = k m (c eq -c) δ = the distance of the mass transfer (cm) δ = the distance of the mass transfer (cm) I L δ δ FLU δ PYR Conclusion: The leaching is not a result of dissolution of PAHs from a free phase of coal tar! D differ approx. 1.1 between the PAHs studied Interpretation of k m HRTs, Holmsund D A km δ V k m = mass transfer coefficient (h -1 ) D = the diffusivity of the solute (cm 2 s -1 ) A = the sorbent surface area (cm 2 ) Holmsund, creosote δ PYR V = the pore water volume (cm 3 ) δ = the distance of the mass transfer (cm) HRT =0.3 h x h x h x 1 δ FLU Conclusion: The leaching may be a result of mass transfer resistance within the solid phase!

7 Leached concentrations, Holmsund Leachable amounts FLU PAH Creosote cont. soil Coal tar cont. soil % leached of total amount Fluorene Phenanthrene Anthracene Fluoranthene Pyrene olubility limitations? olubility limitations? PAH Creosote cont. soil Cmax [µg L -1 ] PAH Creosote cont. soil Coal tar cont. soil Cmax Cmean [µg L -1 ] [µg L -1 ] Fluorene 215 ± Phenanthrene 166 ± Anthracene 26 ± 2 51 Fluoranthene 85 ± 4 68 Pyrene 35 ± 2 47 Fluorene Phenanthrene Anthracene Fluoranthene Pyrene Conclusion: The leaching may be a result of dissolution of PAHs from a free phase of creosote!

8 Conclusions The leaching from the creosote contaminated soil, collected from Holmsund, was probably governed by dissolution. Desorption processes most likely controlled the release of PAHs from the coal tar contaminated soil from Husarviken. -Leached concentrations of the heavier PAHs seemed to be close to distribution equilibrium concentrations, despite the rather short HRT ignificant differences in leaching behaviour, leached concentrations and available amounts although initial concentrations were similar and both samples were aged Leaching tests for organic contaminants can provide valuble information for risk assessments!